Integrated circuit (IC) devices are used in a wide variety of electronic apparatus. IC devices comprise a miniaturized electronic circuit that has been manufactured in the surface of a substrate of semiconductor material. The circuits are composed of many overlapping layers that can be formed by photolithography. Some layers contain dopants that can be diffused into the substrate (called diffusion layers) or ions that are implanted (implant layers) into the substrate. Other layers are conductors (polysilicon or metal layers) or connections between the conducting layers (via or contact layers).
IC devices can be fabricated in a layer-by-layer process that uses a combination of steps, including imaging, deposition, etching, doping and cleaning. Silicon wafers are typically used as the substrate and photolithography is used to mark different areas of the substrate to be doped or to deposit and define polysilicon, insulators, or metal layers. A mask set defines the geometry for the photolithography that is used during fabrication. Each mask set typically contains as many as twenty or more masks, each of which defines a specific photolithographic step in the fabrication process. When the semiconductor devices are an ASIC (application specific integrated circuit) device or a discrete device, a separate mask set is typically created for each process in making that specific product.